Not sure how to find this out but I gather that owners in the Grand Waterfront in To Kwa Wan lease out at times with no agents or so I heard from someone from Europe who was here for one month only.
This geoxpat site has flats by owners - no commission.
Tung Wah Hospitals similar BUT they have an income requirement for their properties (just working on getting a flat there in one of their buildings - clean, older, but suites gutted when tenants leave.) Incomes must be 3x's monthly lease rent. They have listings around HK but I was/am looking in Sheung Wan at 2 BRs. Google that site... in a rush now.